SVN: Add method to find SVN version and use it in svnDiff

We want to enforce the internal diff if possible, but that option
is only in 1.7 and later.

Task-number: QTCREATORBUG-9425
Change-Id: If89f0a7eedae51a04a5f1c40d48287a6425f7a12
Reviewed-by: Tobias Hunger <tobias.hunger@digia.com>

src/plugins/subversion/subversionplugin.h

@@ -106,6 +106,15 @@ public:
                                                 const QString &userName = QString(),
                                                 const QString &password = QString());
 
+    class Version {
+    public:
+        int majorVersion;
+        int minorVersion;
+        int patchVersion;
+    };
+
+    Version svnVersion();
+
 public slots:
     void vcsAnnotate(const QString &workingDir, const QString &file,
                      const QString &revision = QString(), int lineNumber = -1);
@@ -204,6 +213,9 @@ private:
     QAction *m_menuAction;
     bool    m_submitActionTriggered;
 
+    QString m_svnVersionBinary;
+    QString m_svnVersion;
+
     static SubversionPlugin *m_subversionPluginInstance;
 };